- 1. refusal to participate 2. lung disease acute or chronic sPo2 < 92%, PaCO2 > 50 3. renal failure Creatinine > 2 mg% 4. metabolic alkalosis HCO3 > 30 meq/L 5. medication that affect bicarbonate levels: Bicarbonate, Diamox, Fusid 6. obesity BMI > 38 7. congestive heart failure EF < 40 % or clinical signs of congestive heart failure